(a) Technical Field
The present invention relates to a wiper motor control system for a vehicle. More particularly, it relates to a wiper motor control system for a vehicle, which can precisely control a speed of a wiper motor to improve the wiper performance.
(b) Background Art
In general, a wiper device is installed in a vehicle to remove snow, rain, or other foreign substances from a windshield glass and/or a rear window glass. The wiper device is configured to wipe a glass through an operation of a wiper blade moved by a wiper motor, and increase the visibility through the windshield.
Various electronic control systems or sensors, and a plurality of switches have been added to recent wiper devices, so that the wiper device implements a more convenient and safer operation. For example, FIG. 1 is a circuit diagram illustrating a construction of a wiper device for a vehicle. In particular, a BCM (Body Control Module) 10 controls an output of a wiper relay 21 for a control of a wiper motor 11 based on signals of various switches such as an IGN2 switch as inputs.
In general, the wiper device operates the wiper blade, and includes a wiper motor which is configured to generate a rotary torque, a link apparatus which is configured to repeat a certain movement while being linked with the wiper motor, and a parking switch which is configured to control a plurality of sections, e.g., a B+ (operation section), ground (GND) (stop section), and OPEN (dead section).
Further, as shown in FIG. 2, the parking switch 10 of the wiper motor includes a plate 13 integrally rotating along with a rotation of a shaft, and sequentially arranged terminal B corresponding to “operation” and being connected to a multifunctional switch, terminal P corresponding to “stop”, and terminal E connected to a vehicle body from the center of the plate.
Accordingly, as shown in FIG. 3, as a driver controls a multifunctional switch, power is supplied to a wiper motor and the wiper motor is operated on one cycle with ground (GND) (regular position stop section), B+ (operation section), and OPEN (dead section), which rotates the a wiper blade over the windshield of the vehicle.
Further, when the wiper motor is controlled to stop, the wiper motor is operated through the terminal B and terminal P before terminal B of the parking switch is short-circuited, the wiper motor is operated by inertia after terminal B is short-circuited, and the wiper motor is stopped by a connection between terminal E and terminal P when terminal B has short-circuited to finally stop the wiper motor from continuing to rotate.
However, this conventional wiper device has precision control limitations because the wiper motor is operated by a method in which power and GND are supplied to the wiper motor through a mechanical contact by connection of a plate within the wiper motor, and thus inconveniences wiper operations. For example, when a wiper blade switches its direction in an upper portion or a lower portion, a mechanical impulsive sound and an operation noise is generated and the wiping performance of the wiper device is limited because the wiper blade is controlled in a wiper motor operation section at a constant speed.
Meanwhile, some of advanced companies control a wiper motor speed with a pulse width modulation (PWM) control in order to overcome some of the disadvantages of the conventional the wiper device. Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches. In PWM, the average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is. The term duty cycle describes the proportion of ‘on’ time to the regular interval or ‘period’ of time. A low duty cycle corresponds to low power, because the power is off for most of the time. A duty cycle is expressed in a percentage, e.g., 100% being fully on.
However, these systems require that a wiper motor and all the main components of the system, such as the linkage, have to be newly developed and the wiper device cannot be widely applied due to an expensive system such as an H bridge and a Hall Integrated Circuit (IC). Thus, these types of systems are prohibitively costly.